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Flashcards in Forces Acting Across the Membrane Deck (30):
1

What two fluid compartments of the body does the cell membrane separate?

ECF and ICF

2

How permeable is the cell membrane to ions?

Not at all

3

What proportions of Total body water are found in the extracellular and intracellular fluid?

1/3 in the ECF
2/3 in the ICF

4

How do the concentrations of sodium and potassium ions differ in the ECF and ICF?

[K] is high in the ICF and lower in the ECF
[Na] is higher in the ECF and lower in the ICF

5

Are cell membranes rigid or flexible?

Flexible- (oil like)

6

What are the four general classes of membrane proteins?

1. Receptors
2. Transporters
3. Peripheral proteins
4. Enzymes

7

What is the collective name given to receptor proteins, transport proteins and enzymes?

Integral Membrane proteins

8

What is meant by the term 'integral membrane protein'?

A protein which is integrated into the bilayer of the membrane, spanning the hydrophobic core. it cannot be extracted without disturbing the membrane.

9

What is the role of receptor proteins?

Communicate and extracellular signal to the intracellular space to produce a cellular response.

10

What are the two types of transport proteins?

Channel proteins and Carrier proteins

11

Describe how channel proteins allow transport of molecules across the cell membrane.

-Create a continuous pore through membrane, through which specific molecules can flow (usually ions)
- Can be open or gated

12

Describe how carrier proteins allow transport of molecules across the cell membrane.

-Binding of a molecule to the carrier protein causes it to change formation.
-Changes it from being open to ECF to being open to ICF
-Used for transport of larger molecules than channel proteins (e.g. glucose)

13

What is meant by peripheral membrane proteins?

Proteins which are not incorporated into the cell membrane but which are associated with it, on wither the internal or external side.

14

What are the three main roles of peripheral membrane proteins?

- Maintain structure of cell by anchoring cell membrane to intracellular cytoskeleton
- Attach to extracellular matrix
- Perform signalling functions within cells- transmit signals from extracellular to intracellular side.

15

What is the role of membrane carbohydrates?

Recognition of 'self' and 'non-self' material

16

What is meant by the 'electrochemical gradient'?

Sum of the electrical and chemical gradients

17

What are the 5 mechanisms of movement across a cell membrane?

1. Endo/exocytosis
2. Diffusion
3. Mediated transport (facilitated diffusion and active transport)
4. Osmosis
5. Filtration (across capillary walls)

18

Describe the process of endocytosis.

Invagination of cell membrane to enclose molecules in vesicle which eventually pinches off from intracellular side of cell membrane to enter to ICF and migrate to destination.

19

Describe the process of exocytosis.

Fusion of vesicle with cell membrane to release contents extracellularly.

20

What criteria must a molecule meet to diffuse through a lipid bilayer?

Must be a small, uncharged, hydrophobic (lipophilic) molecule

21

What is the difference between a voltage and a ligand gated ion channel?

Ligand gated relies on chemical stimuli, voltage gated relies on electrical stimuli.
Ligand gated channels will open or close depending on whether or not a specific chemical has bound to their receptor binding site.
Voltage gated channels will open or close based on changes in membrane electrical potential.

22

What type of membrane proteins are incorporated into a ligand gated ion channel?

Receptor and transport proteins

23

What is the difference between osmolarity and tonicity?

Osmolarity describes the total number of particles in solution.
Tonicity describes the number of non-penetrating particles in solution. It is this which determines cell volume.

24

What is meant by the term 'hypotonic'?

A solution with fewer non- penetrating particles.

25

What is meant by the term 'hypertonic'?

A solution with more non- penetrating particles.

26

What is the tonicity of normal human ECF?

285 (300) mosmol/ L

27

What is a safe dosage of saline to administer to a patient of normal ECF tonicity?

0.9% 150mM

28

In what direction would water move if a cell was placed in a hypotonic solution?

Water would move into the cell, causing it to swell.

29

In what direction would water move if a cell was placed in a hypertonic solution?

Water would leave the cell, causing it to shrink.

30

What would happen to the volume of red blood cells in a patient with uraemia? (excess urea in their plasma)

It may be expected that the penetrating urea particles would move into the RBCs, creating an osmotic pull and so causing water to also move into the RBCs, increasing their volume.
However, in vivo, plasma contains enough non- penetrating particles to hold water in ECF. Urea will move into RBCs, but water will not follow.